1. Field of Invention
The invention is directed to downhole abrading tools utilized in oil and gas wells to abrade objects within the well and, in particular, to downhole mills that are used to abrade, among other objects, stuck tools, bridge plugs, well tubing, and well casing disposed within the well.
2. Description of Art
In the drilling, completion, and workover of oil and gas wells, it is common to perform work downhole in the wellbore with a tool which has some sort of wearable working profile interfacing with a downhole structure. Examples would be milling a downhole metal object with a milling tool, performing a washover operation with a rotary shoe, cutting through a tubular with a cutting or milling tool, or drilling through formation with a drill bit. During the performance of these operations, it is common for the working profile of the tool, such as the cutting elements mounted on its lower or outer face, to wear away. As this wear progresses, the effectiveness of the tool decreases.
It is desirable to pull the tool from the well and replace it, when the working profile has experienced a given amount of wear. The degree of wear at which it is desirable to replace the tool depends upon the type of tool and the operation being performed. Unfortunately, it is difficult or even impossible for the well operator at the surface of the well to know accurately when this given amount of wear has occurred. Often, the decision as to when to pull the tool depends substantially upon the experience of the operator. That is, the operator must estimate the amount of tool wear based on whatever is known about the time the operation has been underway, the weight on the tool, the type of downhole structure being worked, the cuttings found in the drilling fluid, or a gradual change in work string torque. None of these parameters provides a definitive indication that the wear in the working profile has progressed to a specific degree at which the operator desires to pull the tool from the well. Pulling a tool prematurely adds unnecessary trips out of the well, adding to rig time and increased costs. Pulling the tool too late gradually decreases the effectiveness of the downhole operation, also adding to rig time and increasing the cost of the operation.
Accordingly, downhole abrading tools and methods of indicating to an operator of a downhole abrading tool of excessive wear on a cutting end of the downhole abrading tool have been desired in the art. As discussed herein, the present downhole abrading tools and methods of indicating to an operator of a downhole abrading tool of excessive wear on the cutting end of a downhole abrading tool effectively and efficiently identify excessive wear on the downhole abrading tool. Therefore, the operator of the downhole abrading tool is informed of when the downhole abrading tool should be removed from the well and replaced.